1. Field of the Invention
This invention relates to honeycomb heaters for activating a catalyst used for an automotive catalytic convertor, etc., for purifying exhaust gases.
2. Description of the Prior Art
Conventionally, a heater disposed in a catalytic convertor is described in U.S. Pat. No. 3,770,389, in which a corrugated heater is wound vortically around a central electrode. In this structure, however, as a plurality of corrugated heaters are wound around the central electrode, the corrugated heaters become partly piled up on each other as shown in FIGS. 17(a) and 17(b). Consequently, at some parts of the piled corrugated heaters, deformation of the corrugations and unequal heater density per unit area respectively cause generation of unequal heat. As a countermeasure, it has been suggested that a flat heater and the corrugated heater be alternately disposed. However, since the distance of the corrugated heater between the central electrode and a case holding the periphery of the heater is longer than that of the flat heater, the value of electric resistance of the flat heater is much smaller than that of the corrugated heater. That causes unequal heat generation throughout the whole heater.
To solve the unequal heat generation problem, it has been suggested to use a thin corrugated heater or a thick flat heater which, however, causes a decline of strength of the whole heater or an increase of pressure loss. Accordingly, it is an object of the present invention to provide a honeycomb heater having no deformation of corrugated heaters caused by being piled up and having large heater area per unit area.